MHC class II

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Schematic representation of MHC class II

MHC Class II molecules are found only on a few specialized cell types, including macrophages, dendritic cells and B cells, all of which are professional antigen-presenting cells (APCs).

The peptides presented by class II molecules are derived from extracellular proteins (not cytosolic as in class I); hence, the MHC class II-dependent pathway of antigen presentation is called the endocytic or exogenous pathway.

Loading of class II molecules must still occur inside the cell; extracellular proteins are endocytosed, digested in lysosomes, and bound by the class II MHC molecule prior to the molecule's migration to the plasma membrane.

## Contents

* 1 Structure
* 2 Reaction to bacteria
* 3 Synthesis
* 4 Genes
* 5 External links

## Structure

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Like MHC class I molecules, class II molecules are also heterodimers, but in this case consist of two homologous peptides, an α and β chain, both of which are encoded in the MHC.

Because the peptide-binding groove of MHC class II molecules is open at both ends while the corresponding groove on class I molecules is closed at each end, the peptides presented by MHC class II molecules are longer, generally between 15 and 24 amino acid residues long.

## Reaction to bacteria

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Because class II MHC is loaded with extracellular proteins, it is mainly concerned with presentation of extracellular pathogens (for example, bacteria that might be infecting a wound or the blood). Class II molecules interact exclusively with CD4+ ("helper") T cells (THs). The helper T cells then help to trigger an appropriate immune response which may include localized inflammation and swelling due to recruitment of phagocytes or may lead to a full-force antibody immune response due to activation of B cells.

## Synthesis

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During synthesis, MHC class II is the result of dimerization of α and β chains, with the assistance of an invariant chain.[1]

## Genes

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| Alpha | Beta

|
|

HLA-DM | HLA-DMA | HLA-DMB
HLA-DO | HLA-DOA | HLA-DOB
HLA-DP | HLA-DPA1 | HLA-DPB1
HLA-DQ | HLA-DQA1, HLA-DQA2 | HLA-DQB1, HLA-DQB2, HLA-DQB3
HLA-DR | HLA-DRA | HLA-DRB1, HLA-DRB2, HLA-DRB3, HLA-DRB4, HLA-DRB5

## External links

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* Histocompatibility+Antigens+Class+II at the US National Library of Medicine Medical Subject Headings (MeSH)
* MHC+Class+II+Genes at the US National Library of Medicine Medical Subject Headings (MeSH)

* v
* t
* e

Transmembrane receptors: immunoglobulin superfamily immune receptors

Antibody receptor:
Fc receptor|

| Epsilon (ε)|

* FcεRI
* (FcεRII is C-type lectin)

|

Gamma (γ)|

* FcγRI
* FcγRII
* FcγRIII
* Neonatal

Alpha (α)/mu (μ)|

* FcαRI
* Fcα/μR

Secretory|

* Polymeric immunoglobulin receptor

Antigen receptor|

| B cells|

| Antigen receptor|

* BCR

|

Co-receptor|

| stimulate:|

* CD21/CD19/CD81

|

inhibit:|

* CD22

Accessory molecules|

* Ig-α/Ig-β (CD79)

T cells|

| Ligands|

* MHC
* MHC class I
* MHC class II

|

Antigen receptor|

* TCR: TRA@
* TRB@
* TRD@
* TRG@

Co-receptors|

* CD8 (with two glycoprotein chains CD8α and CD8β)
* CD4

Accessory molecules|

* CD3
* CD3γ
* CD3δ
* CD3ε
* ζ-chain (also called CD3ζ and TCRζ)

Cytokine receptor|

* see cytokine receptors

Killer-cell IG-like receptors|

* KIR2DL1
* KIR2DL2
* KIR2DL3
* KIR2DL4
* KIR2DL5A
* KIR2DL5B
* KIR2DS1
* KIR2DS2
* KIR2DS3
* KIR2DS4
* KIR2DS5
* KIR3DL1
* KIR3DL2
* KIR3DL3
* KIR3DS1

Leukocyte IG-like receptors|

* LILRA1
* LILRA2
* LILRA3
* LILRA4
* LILRA5
* LILRA6
* LILRB1
* LILRB2
* LILRB3
* LILRB4
* LILRB5
* LILRA6
* LILRA5

* v
* t
* e

Surface antigens

Major histocompatibility complex/
Human leukocyte antigen|

| MHC class I|

* HLA-A
* HLA-B
* HLA-C
* HLA-E
* HLA-F
* HLA-G

|

MHC class II|

* HLA-DM
* α
* β
* HLA-DO
* α
* β
* HLA-DP
* α1
* β1
* HLA-DQ
* α1
* α2
* β1
* β2
* β3
* HLA-DR
* α
* β1
* β3
* β4
* β5

* Minor histocompatibility antigen

Other|

* Arrestin
* Calgranulin
* Blood group antigens
* Cell adhesion molecules
* Differentiation antigens

Template:WikiDoc Sources

1. ↑ School of Crystallography The Invariant chain

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